Diatoms in surface sediments of the Gotland Basin in the Baltic Sea

A sediment core, 55 cm long, from station F81 in the Gotland Basin of the Baltic Sea was analysed for diatoms and ebridians. Chrysophyte stomatocysts found in the core were also counted but not identified. The aim was to trace environmental changes, e.g. eutrophication and salinity variations. There is evidence that eutrophication has been increasing in the Baltic Sea in recent decades.Brackish-marine plankton diatoms dominate the entire core and reflect the local planktonic taxa rather well. The dominant taxon is the polyhalobous Actinocyclus octonarius. The main biostratigraphical change within the core analysed takes place at a depth of about 22 cm, where the abundance of diatoms, and especially of Chaetoceros spp., Thalassiosira hyberborea var. pelagica and T. baltica start to increase. This may reflect eutrophication which can be estimated to have started c. 200 years ago.     

Spatial and temporal variation in community composition and photosynthetic characteristics of phytoplankton in the upper Westerschelde estuary (Belgium,SW Netherlands)

Community composition, biomass and primary production of phytoplankton were studied in the east- ernmost section of the Westerschelde estuary in 1984. Photosynthetic characteristics were compared with distribution of some dominant phytoplankton species along a salinity gradient from 5 to 22 Spring phytoplankton, with Cyclotella meneghiniana (freshwater) and Skeletonema costatum (marine) as the dominant species grew faster than summer phytoplankton. In summer, biomass achieved its maximum, due to the riverine Scenedesmus species and the marine diatoms Thalassiosira levanderi and Ditylum brightwellii, as dominants. Growth conditions were more favourable to phytoplankton communities above 15%, than below this salinity. The data were compared with previous studies (1972) of species composition in the area.     

Structural analysis of winter phytoplankton in the Gulf of Naples

Quantitative and qualitative distribution of surface phytoplankton,as related to hydrographic conditions, was studied in the Gulfof Naples in February 1979. Previous work has shown that the Gulf of Naples is a diversifiedecosystem, due to geographic and hydrographic features as wellas man made eutrophication, that can be subdivided into twomajor parts: a coastal subsystem and an open water one. Hydrographic analysis of the winter situation at the surfacefully confirms this picture, as it identifies two distinct watermasses corresponding respectively to surfaced Tyrrhenian IntermediateWater and to Coastal Surface Water. The structural analysisof phytoplankton reveals three assemblages of species characterizingdifferent water types: 1 - the Ischia and Procida channels affectedby the advection of Volturno river and Cuma outfall plumes;2 - the coastal area of the Gulf proper, namely the bays ofPozzuoli, Naples and Castellammare; 3 - the open waterhemislocated beyond the 100 m isobath. The channel area assemblage is dominated by diatoms, particularlyby fast growing species, such as Asterionella japonica, severalspecies of Chaetoceros and Rhizosolenia hebetata f. semispina.The coastal assemblage is identified, among others, by the diatomsCerataulina bergonii, Hemiaulus sinensis; the dinoflagellatesGlenodinium lenticula, Exuviaella compressa and Porella perforata.The open water assemblage is characterized by the diatoms Coscinodiscuscurvatulus and Hemidiscus cuneiformis, the dinoflagellate Amphidiniumacutissimum and the coccolithophore Coccolithus haeckelii.     

Weak 'top-down' control of dinoflagellate growth in the coastal Skagerrak

Effects of planktivorous fish (Sprattus sprartus), copepods(mainly Oithona sp.) and benthic filter feeders (Mytilus edulis)on the biomass and species composition of a natural marine planktoncommunity, dominated by dinoflagellates, was studied experimentallyin September 1988. Plastic 300 I cylinders were filled withSkagerrak surface water, filtered through a 90 µm nylonnet in order to remove mesozooplankton. Copepods were addedin three different concentrations (0, 1x and 6x the ambientdensity) with and without nutrient additions (nitrate, silicateand phosphate). In two nutrient-enriched cylinders with addedcopepods (1x and 6x), 5 cm sprats were also added (10 per cylinder).In two nutrient-enriched cylinders without added copepods. bluemussels (20 per cylinder. 3 cm length) were introduced. Chlorophylla. inorganic nutrients and densities of phytoplankton, ciliatesand copepods were measured throughout the experimental periodof 10 days. Gyrodinium aureolum increased in cell numbers inall but the mussel cylinders, while the other dominating dinoflagellate,Ceratium furca, decreased. This decrease was not due to grazing,but probably a container artefact. Diatoms, Rhizosolenia fragilissinia,Leptocylindrus danicus and Chaetoceros spp., increased slowlyin treatments without fish. In the fish treatments, diatomshad appreciably higher growth rates and cell numbers, probablydue to predation by fish on the copepods. Gyrodiniun aureolunalso had a somewhat higher growth rate in the presence of fish.although this was probably not due to reduction of copepod grazing.The results show that planktivorous fish can affect the biomassand species composition of natural phytoplankton communitiesin marine waters, but that the effect on the late summer-autumndinoflagellate dominated community is weak. Blue mussels areefficient grazers of the whole phytoplankton community and arenot particularly selective with respect to either size or species.     

Description of diatoms from the Southwest to West Greenland coastal and open marine waters

Detailed studies on sub-Arctic and Arctic marine diatom assemblages contribute to the understanding of spatial distribution patterns and their physical drivers. In this study, diatom species were analyzed from water samples collected with a Niskin bottle rosette combined with a CTD along the West Greenland coast (63°58′N–71°08′N and 50°49′W–59°06′W) during summer 2007. Diatom community was represented mainly by three genera Thalassiosira, Fragilariopsis, and Chaetoceros and linked to observed hydrographic and environmental conditions. Thalassiosira spp. were common in coastal waters (particularly Godthåbsfjord) and linked to increased surface water temperature, typical of summer water stratification in West Greenland. Fragilariopsis spp., along with other dominant species associated with higher geographic latitudes, dominated in Arctic fjords (Uummannaq Fjord-Qaumarujuk Fjord). These species generally characterized coastal waters influenced by melting sea ice and/or glacial ice. Chaetoceros spp. were linked to more saline open marine waters, particularly in the Davis Strait south of 70°N, probably corresponding to weaker water stratification and the influence of the West Greenland Current. The present paper provides new knowledge on diatom assemblages along a south–north climate gradient in West Greenland, which is necessary in order to understand how observed ocean-climate changes influence Arctic marine ecosystems. This study provides a reference for palaeoenvironmental reconstructions using diatom microfossils deposited in the West Greenland marine sediments.     

The seasonal distribution of the marine diatom genus Chaetoceros Ehr. in Narragansett Bay, Rhode Island (1981-1982)

The seasonal dynamics of the diatom genus Chaetoceros Ehrenbergwere investigated in Narragansett Bay, Rhode Island. Whole watersamples were collected weekly from July 1981 to October 1982at four locations in the lower Bay and were preserved, concentratedby settling and enumerated. Chaetoceros were most abundant inlate winter–early spring; a second peak occurred in thefall. As in many other temperate neritic areas, C. debilis,C. compressus and C. didymus were major components of die Chaetocerospopulation and could be found throughout the year. Species compositionand dynamics were quite similar at the Jerusalem, GSO Pier andWickford Harbor stations, but were markedly different in PettaquamscuttRiver, a reduced salinity tidal estuary.     

Thalassiosira scotia, sp. nov.: observations on a phytoplankton increase in Early Austral Spring North of the Scotia Ridge

The dominant species in an early spring phytoplankton increasein characteristically antarctic waters north of South GeorgiaIsland is described as Thalassiosira scotia G. Fryx. et Hobanand compared to related species in the South Atlantic, suchas T. antarctica Comber and T. austratis Peragallo. Found ona cooperative US-Argentine cruise of the ISLAS ORCADAS 17–78,T. scotia dominated the phytoplankton in the well-mixed watercolumns of two stations more than 100 km apart. The maximumabu dance of the new species recorded in a discrete water samplewas about 315,000 cells/liter, with up to 18.4 x 10⁹ cells undera m² in the top 100 m, in spite of the fact that there was nowell-marked thennocline to aid in maintaining one water massand thus netaining the population in the euphotic zone. A fewresting spores were noted in one station. The water temperaturein the area was about 1°C, and the salinity 33.9 o/oo.     

Phytoplankton and Nutrients in Goat Island Bay,New Zealand

A quantitative study of the phytoplankton and nutrients in Goat Island Bay, northern New Zealand, was carried out at two stations of depths 7 m and 20 m in 1966-69. There were significant differences in the concentrations of the phytoplankton at the two stations, the deeper station having, in general, higher concentrations than the shallower. Low phytoplankton standing crops were found in winter when the increased run-off from the land resulted in lower salinities, higher turbidity, and higher dissolved silicate levels. The spring growth of diatoms was dominated by small diatoms (Cylindrotheca closterium, Leptocylindrus danicus, Nitzschia pseudoseriata, Phaeodactylum tricornutum, and Rhizosolenia delicatula). Occasionally it was dominated by a population of large centric diatoms (Chaetoceros spp., Coscinodiscus spp., Thalassiosira spp.), but these appeared to be found in a separate water mass which entered the bay and displaced the resident water mass. A third water mass entered the bay in spring and was characterised by the coccolithophore Emiliana huxleyi and a lower temperature. During the summer diatoms dominated the phytoplankton population, but were replaced by dinoflagellates for a short period in autumn.     

Species-specific phytoplankton sedimentation in relation to primary production along an inshore--offshore gradient in the Baltic Sea

The temporal and spatial variability in the quality and quantityof settling phytoplankton material in relation to concurrentprimary production was studied using sediment traps at threecoastal stations from a semi-enclosed bay (Pojo Bay) throughthe outer archipelago to the open Gulf of Finland. The fluxof settling phytoplankton was high (9.3 g C m^–2period^–1)in Pojo Bay, especially in spring, and lower in the archipelago(8.1 g C m^–2 period^–1) and open-sea area (5.2 gC m"2 period"1), although the primary production followed theopposite pattern. A large influx of allochthonous material intoPojo Bay in spring brought allochthonous phytoplankton cellsinto the traps, but limited primary production. Diatoms werethe most abundant settled phytoplankton at all stations, butthe species composition varied between Pojo Bay (Aulacoseiraspp., Rhizosolenia minima) and the outer stations (Skeletonemacostatum, Chaetoceros spp.)At the outer stations, migratingdinoflagellates (Peridiniella catenate) comprised part of thesettling material in spring. The high settling flux of the cyanophyteAphanizomenon flos-aquae is discussed. The species compositionof the phytoplankton assemblage influenced the proportion ofthe total organic carbon sedimentation that consisted of phytoplanktoncarbon.     

Transport of diatom and dinoflagellate resting spores in ships' ballast water: implications for plankton biogeography and aquaculture

Diatom and dinoflagellate species that are not endemic to aregion can be inadvertently introduced when their resistantresting stages are discharged with the ballast-tank waters andsediments of bulk cargo vessels. A survey of 343 cargo vesselsentering 18 Australian ports showed that 65% of ships were carryingsignificant amounts of sediment on the bottom of their ballasttanks. All of these samples contained diatoms, including speciesthat are not endemic to Australian waters. Diatom resting spores,especially of Chaetoceros, were also detected. Dinoflagellateresting spores (cysts) were present in 50% of the sediment samples.Of the 53 cyst species identified, 20 (including Diplopelta,Diplopsalopsis, Gonyaulax, Polykrikos, Protoperidinium, Scrippsiellaand Zygabikodinium spp.) were successfully germinated to produceviable cultures. Such diversity of diatom and dinoflagellatespecies in ships' ballast water suggests that the apparent cosmopolitanismof many coastal phytoplankton species may be due partly to theglobal transport of seawater ballast. Of considerable concernwas the detection in 16 ships of cysts of the toxic dinoflagellatesAlexandrium catenella, Alexandrium tamarense and Gymnodiniumcatenatum. One single ballast tank was estimated to contain>300 million viable A.tamarense cysts, some of which weresuccessfully germinated in the laboratory to produce toxic cultures.These toxic dinoflagellate species, which can contaminate shellfishwith paralytic shellfish poisons, pose a serious threat to humanhealth and the aquaculture industry. Ballast-water quarantinemeasures recently introduced in Australia are discussed. Mid-oceanexchange of ballast water is only partially effective in removingdinoflagellate cysts which have settled to the bottom of ballasttanks. The present work indicates that the most effective measureto prevent the spreading of toxic dinoflagellate cysts via ships'ballast water would be to avoid taking on ballast water duringdinoflagellate blooms in the water column of the world's ports.     

Annual dynamics and production of rotifers in an eutrophication gradient in the Baltic Sea

Spatial and temporal fluctuations in rotifer abundance have been monitored along a trophic gradient in the northern Baltic. The most common rotifer was Synchaeta spp., which had one abundance peak in June and one in September–October. Only during the latter period was the abundance significantly higher in the eutrophic basin compared to the reference area. The annual production of Synchaeta spp. was about double in the eutrophic basin. A positive correlation between Synchaeta spp. biomass and phytoplankton biomass was obtained during the autumn, but not during the early summer peak, although the phytoplankton community was dominated by the same species. Keratella quadrata, K. cochlearis and K. cruciformis were most abundant in August–September, and all three species had increased abundance in the eutrophic basin.     

Spatio-temporal distribution and production of calanoid copepods in the central Baltic Sea

The aim of our study was the exploration of species-specificdistribution and production patterns of dominant copepods inthe Central Baltic Sea (Bornholm Basin). Spatio-temporal distribution,egg and secondary production were studied by means of net-samplingand egg production experiments from April to August 1999. Verticaland horizontal distribution patterns appeared to be linked witheach other and were primarily species-dependent. Both Acartiaspp. and Temora longicornis preferentially inhabited the upper30 m of the water column and the shallower marginal regionsof the Bornholm Basin. In contrast, the C4–5 and C6 ofPseudocalanus spp. preferentially inhabited the halocline region(50–70 m) and the deep central part of the area. Observeddifferences in horizontal distribution among these three copepodsappear to result from different depth preferences and depth-dependentwater circulation patterns. Egg production rates (EPR) clearlyexhibited seasonal differences with maximum EPR in May and minimumEPR in July. Mean EPR was significantly different between species,being highest in Acartia spp. and lowest in Pseudocalanus spp.The variability in EPR was related to differences in hydrographyand modelled food environment.     

Spatio-temporal dynamics of chlorophyll in the open Baltic Sea

Five charts of the chlorophyll and hydrographic fields by verticalprofiles of in situ fluorescence and CTD were made on a stationarygrid of 20 ? 25 nautical miles with a 5-mile spacing in theopen Baltic Sea. Both chlorophyll levels and variability weremaximal close to the spring bloom. High chlorophyll levels insummer are sustained by recurrent nutrient injections from thedeep saline layer. Two of the surveys showed close couplingbetween the coarse-scale (10 km) chlorophyll distribution andthe hydrographic structure determining the intensity of nutrienttransfer. Vigorous advection, stirring and current shear, associatedwith a strong mesoscale eddy, probably dominated the chlorophyllpattern on three surveys. The upward velocities in the cycloniceddy resulted in accumulation of phytoplankton in the aphoticzone. Intensive heat input from the surface caused a suddensinking of the phytoplankton and the formation of a pronouncedsub-surface chlorophyll maximum.     

Temporal patterns and variations in phytoplankton community organization and abundance in Narragansett Bay during 1959-1980

Incident irradiance, surface water temperature and phytoplanktonspecies abundances were measured at weekly intervals in NarragansettBay from 1959 through 1980. Stepwise discriminant analyses (SDA)of this 22-year data set indicate that fundamental ecosystemchanges occurred between the 1960s and 1970s, with 1969 beingthe key transitional year in these decadal shifts in phyto planktontaxonomic structure and seasonal abundance. This decadal shiftwas accompanied by the increased summer abundance of small Thalassiosiraspp., which first appeared in 1966 and by 1969 became the sixthmost important phytoplankton component in this bay. Decadaltrends in phyto plankton community organization and abundancewere also accompanied by distinct long-term climatological gradientsof temperature and light. The 1960s were generally colder andbrighter than the 1970s. Prior to 1969, the annual phytoplanktonmaximum occurred most commonly during winter; in the 1970s,the annual maximum generally shifted to a summer event. Three5-year phytoplankton cycles occurred between 1959 and 1974.During each pentade, the phytoplankton community returned toa similar taxonomic organization and abundance cycle after divergingin the intervening years. Pentade cycles did not occur after1974; the phytoplankton community thereafter diverged significantlyfrom each preceding year. Five species [Skeletonema costatum,Detonula confervacea, Asterionellopsis glacialis, Hererosigmaakashiwo (= Olisthodiscus lureus) and Thalassiosira nordenskioeldii]dominated the phytoplankton over the 22-year period. SDA revealeda high degree of similarity and constancy in the annual occurrencepatterns of these taxa. The decadal shifts revealed by SDA weremore directly related to the considerable interannual variabilitythat characterized the abundance and seasonality of the lessabundant species.     

Horizontal Variation of Bacterioplankton in the Baltic Sea

Variations in the thymidine incorporation rate, bacterial abundance, and mean cell volumes in the surface water (0.5 m) of the Baltic Sea in spring and summer were compared in studies with different spatial scales (570 nautical miles [nmi] [ca. 1056 km], 220 nmi [ca. 407 km], 24 nmi [ca. 44 km], 12 nmi [ca. 22 km], and 200 m). The objective of the comparison was to investigate whether a single sample taken at one sampling point is representative enough for researchers to make generalizations about a larger water area. Bacterioplankton variation was connected more to seasonal characteristics than to the spatial scale of sampling. Variation was greater and more random in spring than in summer. The state variables (bacterial abundance and mean cell volume) varied less than the rate variable (thymidine incorporation). The results suggest that the sampling design for bacterioplankton studies in northern temperate seas should be planned primarily according to the season and that more stress should be put on rate variable measurements than on those of state variables.     

Unattended monitoring of potentially toxic phytoplankton species in the Baltic Sea in 1993

Variabilities in chlorophyll a fluorescence, temperature andsalinity in the surface were recorded unattended on board twomerchant ships in the Baltic Sea. When these recordings werecomplemented by automated water sampling, it was possible toanalyze the phytoplankton species composition in 426 samples.In total, 22 potentially toxic phytoplankton species or generawere detected. Nodularia spumigena was the only species thatformed extensive blooms The system has proved to be an effectiveearly warning method for exceptional and eventually harmfulalgal blooms. The possibilities for using this method as analternative, or a complement, to conventional methods in marinephytoplankton monitoring are discussed.     

Changes in photosynthetic activity of the diatom Phaeodactylum tricornutum in a culture of limited volume

Changes in photosynthetic activity of a marine diatom duringalgal growth were studied with a typical culture medium formarine algae, ASP-2 (l). As the algal specimen, Phaeodactylumtricornutum was used for the experiments. Nitzschia closteriumand Chaetoceros sp. were also supplementarily used. Photosynthetic and p-benzoquinone Hill activities remarkablychanged with time during algalgrowth; with maximum activityfound in cells at log phase. A rapid decrease occurred in theinterphase from the log to stationary phase. The activity changewas not accompanied by variation in photosynthetic pigment content. The low concentration of phosphorus source was suggested asthe main cause for the change. On supply of extra inorganicphosphate, the time length for holding high photosynthetic activitybecame longer; or, the activity of the cells at stationary phaserecovered at least partly even in the dark. Dark recovery wasnot accompanied by either algal growth or an increase in thecontent of photosynthetic pigments. Inactivation of photosynthesis in the stationary growth phaseand activation by added phosphate in the dark were inferredto be due to changes in activities of both the CO₂-fixing andelectron transfer systems. The observed activity change maynot be attributable to a deficiency in inorganic phosphate asthe substrate for photophosphorylation. Similar changes in photosynthetic activity were also observedwith Nitzschia closterium and Chaetoceros sp. (Received January 30, 1971; )     

The effects of nitrate and phosphate enrichments on the phytoplankton from Marsaxlokk Bay,Malta (Central Mediterranean)

The technique of artificial enrichment of seawater has been employed in an attempt to define nutrients critically limiting the growth of phytoplankton in Marsaxlokk Bay, Malta. While both nitrates and phosphates are scarce, phosphate is the primary factor limiting phytoplankton growth. There appear to be no seasonal changes in the respective roles of phosphates and nitrates as factors limiting primary productivity. The higher incubating temperatures of theJune cultures resulted both in a quicker attainment of the peak values of chlorophyll a and in a higher peak concentration of this pigment as compared with the November and February experiments. There appeared to be no major changes in the relative composition of the phytoplankton populations in all enrichment experiments. Diatoms, mainly Skeletonema costatum and Chaetoceros spp., dominated all culture vessels. These results are discussed in the light of the values obtained for the ratio of pigment absorption at 430 nm to that at 665 nm.     

121 Influence of Benthic vs. Pelagic Seeding on Coastal Diatom Bloom Development

Diatom blooms may be initiated by cells that have survived in the plankton or germinated resting stages from the sediments. However, it is not well understood how these different inocula contribute to bloom development. We followed diatom community development in twenty‐liter microcosms given different inocula. Surface sediment and phytoplankton were collected in Gullmar Fjord, Sweden. Replicate microcosms were then dosed with local sediment and/or plankton and incubated in situ in Gullmar Fjord. We also followed the concurrent development of the phytoplankton community in the fjord. Experiments run in both spring and fall 2002 showed that bloom development in the microcosms was significantly faster when seeded by planktonic cells. However, addition of sediment may have stimulated planktonic growth and also provided additional propagules. The type of inoculum used strongly influenced the diatom composition in the microcosms. Sediment additions, through germination of resting stages, resulted in communities dominated by Detonula confervacea and Thalassiosira minima in spring, and Skeletonema costatum in fall. Planktonic inocula resulted in blooms of T. nordenskioeldii and Chaetoceros debilis in spring, and S. costatum and several Chaetoceros spp. in fall. Microcosms dosed with both plankton and sediment showed a mixed species assemblage. Comparisons between the microcosms and fjord phytoplankton suggest an important role for benthic seeding of diatom blooms.     

Diatom taphocoenoses in the coastal upwelling area off South West Africa

The diatom floral composition of 124 sediment samples from the South East Atlantic records the influence of coastal upwelling on sediment composition off South West Africa. Inner shelf samples between 19° and 24°S are rich in diatom valves and the patterns of diatom species distribution in these samples are related to the coastal upwelling process. Comparison with recent phytoplankton data shows that the sediment assemblages preserve many of the important species of the diatom biocoenoses, including Chaetoceros (resting spores), Delphineis karstenii, Thalassiosira eccentrica, and Thalassionema nitzschioides. Delphineis karstenii, a pioneer species in enriched coastal water, occurs nearshore and Chaetoreros resting spores are widespread, with highest relative abundance values in some more offshore samples. The abundance of the Thalassiosira eccentrica group and of Thalassionema nitzschioides in sediment samples in and near Walvis Bay reflects the recurrence of intense upwelling off this part of the coast. An abundance of large centric species has been reported in hydrological conditions characteristic of newly upwelled waters and, correspondingly, Actinocyclus octonarius and some large Coscinodiscus species occur in the sediments in nearshore patches or belts.